It has been known that ultraviolet irradiation of titanium dioxide used as a photocatalyst causes the generation of highly oxidative hydroxy radicals (OH radicals), which has been used to eliminate organic substances such as organic compounds and bacteria. As a titanium dioxide excitation source other than ultraviolet rays, ultrasonic waves have drawn attention. It has been reported that low-frequency ultrasonic waves bring about the same bactericidal effect as ultraviolet rays do (see Non-patent Document 1).
This has been applied mainly in environmental fields, and such a technique has been known as to improve water quality and eliminate water microorganisms by irradiating titanium dioxide with ultrasonic waves. For example, for the purpose of providing a simply-structured sterilization apparatus and a sterilization method with significant effects of sterilizing fluids, Patent Document 1 discloses: a fluid sterilization apparatus including a flow channel along which fluids flow, an ultrasonic transducer, and an ultrasonic response diffuser; and a sterilization method. The technique of Patent Document 1 uses, as the ultrasonic response diffuser, a substance (e.g., titanium dioxide) that exhibits photocatalytic action when irradiated with ultrasonic waves, and sterilizes the fluids by irradiating the ultrasonic response diffuser with ultrasonic waves.
Further, the bactericidal effect of ultrasonic irradiation of titanium dioxide has been confirmed by the fact that the concentration of Escherichia coli decreased when titanium dioxide was excited by ultrasonic waves with an output of 200 W at a frequency of 39 kHz (see Non-patent Document 1).
Further, Patent Document 2 discloses a method for producing hydroxy radicals through ultrasonic irradiation of water containing titanium dioxide particles.
Further, for the purpose of degrading organic constituents or, in particular, persistent hazardous organic compounds present in the water and detoxifying pathogenic microorganisms present in the water, Patent Document 3 discloses: a water treatment method for, during ultrasonic irradiation of water in which titanium dioxide exists, adding an antioxidant such as hydrogen peroxide into the water being treated; and an apparatus that is used for the method.
Further, for the purpose of providing a method for treating an organic substance, Patent Document 4 discloses a method for irradiating an organic substance with ultrasonic waves in the presence of an organic-substance treating agent. Examples of the organic substance encompass fungi, bacteria, and viruses, and examples of the organic-substance treating agent encompass titanium oxide deficient in oxygen.
Further, Patent Document 5 discloses a liquid treatment method characterized in that a liquid, containing organic matter, which is to be treated is irradiated with ultrasonic waves in the presence of titanium oxide composite woody carbide and hydrogen peroxide and the organic matter is thereby degraded.
In addition to the foregoing techniques, examples of techniques that involve the use of ultrasonic waves and titanium oxide encompass the following techniques. For example, Patent Document 6 discloses a method and apparatus for treating organic-pollutant-containing waste water through oxidative degradation of organic pollutants in a radical reaction by hydroxy radicals. The hydroxy radicals here are electrically generated by using titanium dioxide as a positive electrode. Further, ultrasonic waves are used to overcome such a disadvantage that a considerable amount of energy is used to charge suspended particles contained, if any, in waste water being treated and such a disadvantage that a radical-generating reaction is significantly slowed down due to deposition of a large number of particles in a hole of a metal oxide electrode.
Further, Patent Document 7 discloses a cosmetic tool that concurrently generates ultrasonic waves and far-infrared rays by passage through a titanium oxide head or a metal plate. Although Patent Document 7 gives no examples and therefore lacks clarity about principles or mechanisms, Patent Document 7 says that the ultrasonic output is activated by passage through the titanium oxide plate and the promotion of a massaging effect is thereby achieved.
Incidentally, there has been an issue of bacterial infection due to contamination of skin openings by medical devices such as intracorporeal indwelling catheters, gastrostomy catheters, and tracheostomy tubes. When implanted in a living organism, an intracorporeal indwelling catheter or the like is recognized as a foreign object by the living organism's tissue. Moreover, the living organism's tissue and the medical device do not make close contact with each other. Therefore, for example, in the case of a percutaneous catheter, the epidermis is pushed inward along the catheter, i.e., there occurs epithelial downgrowth (which is a phenomenon that causes the epithelial tissue to invaginate along a surface of the catheter). Moreover, deepening of the epithelial downgrowth renders sterilization incomplete and causes the formation of a route of bacterial infection, thus causing inflammation of the skin. Eventually, there is no alternative but to dislodge the intracorporeal indwelling catheter. In order to solve such a problem, there has been proposed various intracorporeal indwelling medical devices designed to make close contact with living organisms.
For example, an intracorporeal indwelling catheter such as an interperitoneal indwelling catheter or a central venous catheter includes a cuff member (Dacron cuff), made of Dacron unwoven cloth, which serves to prevent bacterial infection and fix the catheter in a living organism (e.g., see Patent Document 8). Subcutaneous implantation of the Dacron cuff leads to proliferation of subcutaneous connective tissue, with the result that the catheter is fixed so firmly as to be less likely to be dislodged by accident. However, even in the case of such a catheter, the Dacron cuff does not make close contact with the living organism's tissue, and therefore cannot completely prevent bacterial infection.
Further proposed as an intracorporeal indwelling medical device is a percutaneous terminal made of a highly biocompatible hydroxyapatite ceramic (see Non-patent Document 2). According to the arrangement of Non-patent Document 2, the percutaneous terminal is constituted solely by a hydroxyapatite ceramic. Hyrdorxyapatite is a component of a tooth and exhibits an excellent affinity for soft tissue. However, hydroxyapatite is hard and fragile. Therefore, the percutaneous terminal is hard and, when implanted in a living organism, may leave space between the hydroxyapatite ceramic and the living organism's tissue. That is, the percutaneous terminal makes poor contact with the living organism. Furthermore, manufacture of a percutaneous terminal solely from a hydroxyapatite ceramic causes an undesirable increase in size of the percutaneous terminal. As such, the arrangement of Non-patent Document 2 is riddled with various problems. For example, the percutaneous terminal is fragile. Further, when implanted in a living organism, the percutaneous terminal brings discomfort to the patient because of its hardness.
[Patent Document 1]
    Japanese Unexamined Patent Application Publication No. 275842/2007 (Tokukai 2007-275842; published on Oct. 25, 2007)[Patent Document 2]    Japanese Unexamined Patent Application Publication No. 26406/2003 (Tokukai 2003-26406; published on Jan. 29, 2003)[Patent Document 3]    Japanese Unexamined Patent Application Publication No. 351331/2004 (Tokukai 2004-351331; published on Dec. 16, 2004)[Patent Document 4]    Japanese Unexamined Patent Application Publication No. 30031/2008 (Tokukai 2008-30031; published on Feb. 14, 2008)[Patent Document 5]    Japanese Unexamined Patent Application Publication No. 288302/2005 (Tokukai 2005-288302; published on Oct. 20, 2005)[Patent Document 6]    Japanese Translation of PCT Patent Application Publication No. 538960/2002 (Tokuhyo 2002-538960; published on Nov. 19, 2002)[Patent Document 7]    Japanese Unexamined Patent Application Publication No. 19177/2003 (Tokukai 2003-19177; published on Jan. 21, 2003)[Patent Document 8]    Japanese Unexamined Patent Application Publication No. 206193/1996 (Tokukaihei 8-206193; published on Aug. 13, 1996)[Non-patent Document 1]    Shimizu, N., Ogino, C., and Dadjour, M. F.: “Chô-onpa to nisankachitan wo mochiita yûgaibusshitsu no sakkin (Sterilization of hazardous microorganisms with use of ultrasonic waves and titanium dioxide)”, Chô-onpa Riyôgijutsu Shûsei (Corpus of Ultrasonic Techniques), NTS, p. 115-125, 2005.[Non-patent Document 2]    Aoki, H.: “Medical Applications of Hydroxyapatite”, (Ishiyaku EuroAmerica, Inc., 1994), p. 133-155.